Various devices are currently known to increase the aerodynamic efficiency of a truck, semi trailer, or other large moving object. It has long been recognized that the rectangular high profile shape of these vehicles and the speeds necessary for travel increase the amount of air drag. Reducing the effects of air drag has the greatest potential to reduce overall fuel consumption. The disclosure relates to add-on aerodynamic air deflectors for the rear surface or leeward face of a transport trailer. For example, the air deflector boattails can be mounted to swing-doors on a box van or other long haul transport trailers.
Inflatable drag reducers have been described (e.g. McDonald (1477) U.S. Pat. No. 4,006,932, Ryan (1498) U.S. Pat. No. 5,823,610, Andrus (2002) U.S. Pat. No. 6,409,252), and are more practical than rigid versions (e.g. Lechner (1494) U.S. Pat. No. 5,375,903, Switlik (1496) U.S. Pat. No. 5,498,059, Boivin (2001) U.S. Pat. No. 6,257,654 B1), because inflatables are light-weight and can be collapsible to a very thin state so as not to interfere with complete trailer door opening which is important because of the limited room to maneuver at most loading docks. However, given that the majority of standard long-haul box van transport trailers are typically a double door (i.e. swing door) configuration, it is beneficial to have a drag reducer with two separate portions (a separate portion associated with each door). Additionally, the two separate portions should, as a coordinated unit, provide beneficial drag reduction. It is also beneficial for the external surfaces over which the airstream passes to be substantially planar for minimum turbulence creation and maximum drag reduction. Inflatables naturally tend towards a spherical or curved shape without an internal means of controlling, for example, bulging of the external surfaces.
It is of course well known that the box shape of trailers of tractor-trailer vehicle combinations, and other truck-trailer combinations, is the result of a need to optimize cargo space therewithin, and it is likewise well known that the boxlike configuration is not aerodynamically efficient. The aerodynamic drag resulting from the box shape accounts for a considerable percentage of the fuel consumption of large trucks and tractor-trailer vehicle combinations during highway operation thereof. In an effort to improve the operating efficiency of such vehicles, the tops of the cabs of trucks and tractors and the upper forward ends of both the tractor and trailer have been streamlined by using a wide variety of body contours and wind foil devices. For the same purposes, the rear ends of transport trailers have been provided with inflatable drag reducing devices or bladders such as those shown, for example, in U.S. Pat. No. 4,006,932 to McDonald, U.S. Pat. No. 4,601,508 to Kerian, U.S. Pat. No. 4,702,509 to Elliott, U.S. Pat. No. 4,741,569 to Sutphen, and U.S. Pat. No. 6,409,252 to Andrus.
Air foils mounted on the cabs of trucks and trailers can be rigid and permanent in character in that the areas on which the air foils are mounted do not need to be accessed in connection with use or operation of the vehicle. On the other hand, the rear ends of trailers do have to be accessible in that they are closed by doors providing access to the interior thereof for loading and unloading purposes. Accordingly, aerodynamic and drag reducing devices designed for use on the rear ends of trailers can be detachable as shown in the patent to Elliott or provided individually on the doors of the trailer as shown in the other patents referred to above. As disclosed in Elliott, if the device is not going to be used it would have to be stored somewhere in the vehicle or, in the manner of the devices disclosed in the patents to McDonald, Kerian, Sutphen, and Andrus, merely deflated and allowed to remain on the door. Removal and storage is a labor intensive and time-consuming operation in addition to requiring storage space.
For these reasons inflatable drag resistors (i.e. boattails) have become exemplary because they are light, inexpensive, and may be collapsed without the use of an excessive number of moving parts, examples of such devices are disclosed in U.S. Pat. No. 4,978,162 to Labbe, U.S. Pat. No. 5,236,347 to Andrus, U.S. Pat. No. 5,375,903 to Lechner and U.S. Pat. No. 5,823,610 to Ryan et al. However, despite the preference of inflatable boattails, not many are in use because they still tend to fail in solving the problems currently associated with loading and unloading the tractor-trailer because the wind dam is attached as one unit to the back. (See Lechner, Andrus).
The devices currently known to increase aerodynamic efficiency, while somewhat effective, suffer from a number of other drawbacks. The previous devices, heretofore known, have been attached to the back of trailers often include loose pieces that must be attached and removed to accommodate loading and unloading. As a result, the pieces are easy to lose, and are time-consuming to assemble because they are heavy and bulky making them difficult to both attach and remove. Similarly, other devices do not allow for the convenient loading and unloading of the trailer's cargo because they consist of a single attached unit that must be removed in order to open and close the trailer doors. Furthermore, often the prior art devices are ineffective in that they provide little drag reduction when in use or are costly to produce and install.
Accordingly a need exists for an improved wind dam device for effectively reducing the air drag of a tractor-trailer.